1. A fixed point theorem in Banach space;Altman;Bull. Acad. Pol. Sci. Cl. III,1957
2. Firmly nonexpansive mappings in classes of geodesic spaces;Ariza;Trans. Amer. Math. Soc.,2014
3. Metric Spaces of Non-Positive Curvature;Bridson,1999
4. Spaces with nonpositive curvature;Busemann;Acta Math.,1948
5. The Geometry of Geodesics;Busemann,1955